Sathya Chinnadurai1 and Nora Matthews2,3 1 Saint Louis Zoo, 1 Government Drive, Saint Louis, MO, 63110, USA 2 Department of Small Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, 408 Raymond Stotzer Pkwy, College Station, TX, 77845, USA 3 Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, 930 Campus Road, Ithaca, NY, 14853, USA Animals discussed in this section can fall into four broad categories, domesticated donkeys and mules, domesticated horses, that by nature and training are not able to be handled in a routine manner (rodeo horses), feral horses (mustangs), and truly wild species (e.g. zebra). Working with any of these animals requires a special understand of unique aspects of physiology, pharmacology, and handling that are distinct from other horses. Previous articles (Matthews et al. 2005) and book chapters (Matthews 2009) have covered some of the differences in physiology, behavior, and pharmacology which exist between donkeys and horses. These species‐related differences have numerous implications for anesthetic and analgesic strategies in donkeys. For instance, the donkey’s relative lack of flight response contributes to its reputation for stubbornness; when confronted with an unknown and unevaluated obstacle, a donkey will freeze until it has had a chance to assess the risk associated with it. Attempts to push or scare the donkey forward (commonly used in horses) are generally unsuccessful; however, time is generally effective. Numerous publications have appeared that discuss differences in pharmacokinetics of anesthetics and analgesics (Coakley et al. 1999; Mealy et al. 2004; Sinclair et al. 2006; Taylor et al. 2008; Matthews and Thiemann 2015), while at the same time, much of the available knowledge on donkeys is from clinical experience and does not come from scientific research. Preoperative evaluation of the donkey should be as thorough as it would be for a horse, including an accurate estimate of body weight (Appendix 3: Heart Girth Nomogram, The Professional Handbook of the Donkey, 4e, 2008). It is critically important to recognize that normal parameters for temperature, respiratory, and heart rates as well as hematological and biochemical parameters (Appendix 1, The Professional Handbook of the Donkey, 4e, 2008) may be significantly different than in horses. Normal values for adrenocorticotropic hormone (ACTH) and insulin are significantly different for donkeys as compared to horses, while other values (e.g. cortisol) are not different (Dugat et al. 2010). Many normal values for mules have not been established, so caution should be used when interpreting blood work. Preoperative assessment and treatment of pain should also be diligent; donkeys may not exhibit pain as openly as horses, so severe pain may be present which should be treated prior to anesthesia (Regan et al. 2016). In the author’s experience (NM), failure to adequately treat pain preoperatively may lead to cardiovascular decompensation after induction of anesthesia. Appropriate use of non‐steroidal anti‐inflammatory drugs (NSAID‘s) are well reviewed in other sources (Grosenbaugh et al. 2011). In general, NSAIDs are very effective in donkeys, but dosing intervals should be shorter as most are metabolized more rapidly in donkeys than in horses. Although some differences between sizes/breeds of donkeys have been documented for analgesics such as phenylbutazone, as well as injectable anesthetics (Matthews et al. 2001), there is really very little information about many other breeds of donkeys throughout the world. Comparative studies of drugs such as tramadol, which has been shown to have low bioavailability in Italian donkeys (Giorgi et al. 2009) might show differences in other breeds. Donkeys are also more likely to be hyperlipemic when stressed or ill; hyperlipemia needs to be treated as early as possible to ensure survival of the patient. Jugular catheterization is facilitated by use of good restraint; a donkey or mule should be tied short to an unmovable object. When necessary, restraint with ropes, hobbles, or squeeze gate can be used similar to what might be used with cattle. Donkeys and mules are much less likely to fight restraint (although they will try it out), allowing procedures to be performed with less trauma to all. An intravenous catheter must be long enough (the author prefers at least 9 cm or more) to penetrate the thicker skin and fascia of the donkey while still remaining within the vein. Although the jugular vein is in the same location as in the horse, it is covered by the cutaneous colli muscle, which is thicker than in the horse (Herman 2009) as well as a fascial layer. This may make it more difficult to visualize the vein, and the catheter may need to be introduced at a slightly different angle compared to the horse. Use of a lidocaine “bleb,” placed subcutaneously over the vein, is recommended for increased tolerance to catheter placement. Transdermal lidocaine can be used for donkeys (or mules) which are “needle shy,” 20–30 minutes must be allowed for sufficient transdermal absorption to anesthetize the skin. Choices for sedation and premedication were previously reported (Matthews et al. 2005). Since that publication, an additional report has described the pharmacokinetics of xylazine in mules compared to horses (Latzel 2012). The half‐life of xylazine in mules was 15 minutes shorter than in the horse, and the horse dose did not provide sufficient sedation. It is recommended that the dosage of xylazine for mules should be 1.5 times greater than the dosage needed in horses. This is consistent with the authors’ experience with sedation of mules, but not required for donkeys. The recent introduction of detomidine oral gel has been found to be very useful for donkeys and mules which are difficult to inject (NM, personal observation); the label dose appears to provide good sedation in donkeys when adequate time (40 minutes) is allowed for absorption. Numerous drug combinations have been used for induction and maintenance of donkeys and mules with injectable drugs (Matthews et al. 2005). Intermittent boluses of xylazine and ketamine can be used, but may need to be given more frequently than in horses; approximately every 10 minutes, compared to 15–20 minutes in horses particularly for donkeys since they metabolize ketamine more rapidly. One study evaluated various combinations of guaifenesin with xylazine and ketamine (Taylor et al. 2008) and found that GKX (guaifenesin 50 mg/ml, ketamine 2 mg/ml, xylazine 0.5 mg/ml) produced satisfactory anesthesia following premedication with 1.1 mg/kg xylazine. Induction was accomplished by rapid gravity administration of the mixture until the donkey became recumbent, then the infusion was slowed and maintained as indicated by monitoring anesthetic depth (approximately 1.5 ml/kg/h). For larger donkeys and mules, where restraint of the patient during induction might be difficult, a xylazine/ketamine induction can be used, and then the GKX mixture started for maintenance. This mixture can be used when transport of the patient is required. Thiopental has been described for induction (7 mg/kg intravenous [IV]) and maintenance (8 mg/kg) of anesthesia in donkeys for 100 minutes after premedication with atropine, acepromazine, and xylazine (Emami et al. 2006). Induction and maintenance quality were reported to be good, but recovery was slow; standing time was 92 minutes after anesthesia was concluded. Propofol has been reported for use as an induction agent in donkeys (Matthews et al. 2005). An additional report compared propofol bolus (2 mg/kg) to thiopental bolus (10 mg/kg) after premedication with xylazine (1.0 mg/kg) (Abd‐Almaseeh 2008). Induction time was slightly faster and of better quality with thiopental, but recovery was considered to be better with propofol. Apnea was observed with thiopental, but not with propofol. Propofol (1 mg/kg) combined with ketamine (2 mg/kg) and compared to ketamine alone (3 mg/kg) after premedication with xylazine (1.0 mg/kg) has been described (Abass et al. 2007). The combination of ketamine and propofol produced a smoother induction, better muscle relaxation, longer anesthesia time, and smoother recoveries than ketamine alone. Maintenance with inhalational anesthesia is recommended for longer procedures (>60 minutes) and for older or sicker patients. Endotracheal intubation can usually be achieved blindly, although it may be slightly more difficult than in horses, due to anatomical differences in the donkey (Herman 2009). Halothane, isoflurane, or sevoflurane can be used; no apparent differences in minimum alveolar concentrations have been noted between horses and donkeys. Heart and respiratory rates, blood pressure, eye signs, and muscle relaxation should all be monitored. Respiratory rates are usually higher in anesthetized donkeys than in horses and respiratory depression seen with isoflurane in horses does not appear to be as great a problem in donkeys, i.e. the “breath‐holding” seen in horses during isoflurane anesthesia does not prohibit the use of isoflurane in donkeys. Blood pressure appears to be the most reliable indicator of depth of anesthesia in donkeys; rapid increase usually indicates the patient is light and likely to move. Blood pressure can be measured indirectly using a cuff or directly using an arterial catheter attached to an aneroid manometer or transducer. Percutaneous placement of the arterial catheter is facilitated by cutting through the skin with a sterile needle before introducing the catheter to prevent “burring” of the catheter by the thick skin and fascia. A branch of the maxillary artery or lateral metatarsal artery is easiest to catheterize, but large auricular arteries are also available. Administration of intravenous fluids (such as lactated Ringer’s solution) is recommended at 5–10 ml/kg/h, especially during inhalational anesthesia, to support blood pressure. Appropriate positioning to protect radial and peroneal nerves and padding to prevent myositis is also recommended. Myositis appears to be less of a concern in donkeys than in horses (presumably because of smaller muscle mass), but prevention is still wise (especially in larger draft mules). Butorphanol (0.02–0.04 mg/kg/h), ketamine (0.4–0.6 mg/kg/h) or lidocaine (1.5 mg/kg/h) can be used to provide intraoperative analgesia when needed, but there is no information specific to the use of these drugs in donkeys compared to horses; clinical judgment must be used. Local blocks (with lidocaine or bupivacaine) can also be used for specific procedures (e.g. pastern arthrodesis, castration) to achieve analgesia. Transdermal fentanyl patches have been used on donkeys and may be effective for some types of pain; however, information specific to analgesia in donkeys is greatly needed. The pharmacokinetics of tramadol have been reported, but no information about efficacy is available (Giorgi et al. 2009). In general, there is a lack of information on the use of analgesics, especially opioids, in the donkey. Donkeys usually recover well from anesthesia, but often take longer to attempt standing than horses. As with horses, attention must be paid to ensure a patent airway; “snoring” noises may indicate partial airway obstruction which can be relieved by straightening the donkey’s head and neck or passing a small nasogastric tube into the upper airway. Lack of analgesia can produce a rough recovery, but donkeys are not prone to becoming hysterical in recovery as horses are. Many donkeys will require assistance to stand by lifting on the tail and some may rise hind end first similar to a bovid while others will rise in the same manner as a horse. As might be expected, mules can follow either their donkey or horse lineage when recovering; therefore, it is difficult to predict how an individual animal will rise during recovery. Local anesthetic techniques can be beneficial in a modern multi‐modal anesthetic approach (Lamont 2008). Both during general anesthesia and in standing surgical procedures, these techniques can be a valuable addition. Local anesthetic techniques similar to those used in horses will likely be successful; however, minimal research has been performed evaluating most of them. Epidural anesthesia has been described in the donkey (Shoukry et al. 1975). Most common indications include rectal or vaginal prolapse or to treat melanomas in the tail and perineal region, but it can also be used for long‐term analgesia after hindlimb surgery or with painful conditions in the hindlimb like septic arthritis. A thorough description of the anatomy of the sacral and coccygeal vertebrae of the donkey is available (Burnham 2002). The first intercoccygeal space in the donkey is narrower than the second and, therefore, the latter is more suited for caudal epidural puncture. The needle can be directed at an angle of 30° from the horizontal and can be introduced into the vertebral canal, because there are no large tail muscles. The spinal processes of the sacral and coccygeal segments are more easily palpated in the donkey compared to the horse (Burnham 2002). In order to perform standing surgery in donkeys, proper sedation is a first requisite. Sedative and analgesic effects of detomidine have been described in donkeys (Mostafa et al. 1995). Detomidine at 5–10 mcg/kg provides adequate sedation whereas increasing the dosage to 20–40 mcg/kg provides sedation and strong analgesia. While donkeys seem to have similar clinical effects to alpha‐2 agonists, mules require approximately 50% more xylazine, compared to donkeys and horses (Matthews et al. 1997). Higher requirements for romifidine were also reported in untamed mules (Alves et al. 1999). Protocols for standing surgery can be composed of sedatives in constant rate infusions (CRI), combined with systemic opioids and local anesthetic techniques. Protocols used in horses have been used successfully in donkeys as well (Van Dijk et al. 2003). For example, laparoscopic ovariectomy in standing donkeys using xylazine sedation and local infiltration of the laparoscopic portal sides with lidocaine has been described (Aziz et al. 2008). This protocol could also be combined with epidural morphine (0.1 mg/kg) for additional analgesia, a technique that is described for horses (Van Hoogmoed and Galuppo 2005). Adding epidural morphine to this standing anesthesia protocol led to decreased surgical time, improved patient comfort, and reduced the sedation needed to perform ovariectomy. Although, not handled in the conventional horseman’s manner, rodeo horses are used to being around humans, wearing halters, are extensively transported and used to standing in cattle chutes (Figure 14.1). Depending on the equipment available, it is possible to sedate them intramuscularly or intravenously with an alpha‐2 agent (e.g. xylazine or detomidine) in a chute. Doses for sedation depend on route of administration and are generally larger than would be used for a more handled horse. One author (NM) has seen and sedated rodeo horses with twice normal doses of xylazine or detomidine; induction is then possible in the chute with IV diazepam‐ketamine at normal doses. The horse’s head can be controlled during induction with a halter rope and intravenous catheter placed immediately after induction (Figure 14.2). The horse can then be transported to surgical area using “triple‐drip” for maintenance of anesthesia and a horse‐slide (or movable table). This process is reversed when surgery is completed; the horse is transported to a recovery area, or pen adjacent to the chute, or stall from which the horse can be returned to handling areas after recovery. Mustangs and other feral horses, while from a similar lineage as the domestic horse breeds, have not been managed or trained for working and can behave similar to a wild equid. Numerous references exist for darting feral horses with more modern drug combinations (Hampton et al. 2016; Matthews and Myers 1993; Woolnough et al. 2012; Zabek et al. 2014).
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Anesthetic Management of Other Domesticated and Non‐Domesticated Equids
Introduction
Domesticated Donkeys and Mules
Pre‐anesthetic Evaluation and Patient Preparation
Intravenous Catheterization and Premedication
Induction and Maintenance with Injectable Anesthetics
Maintenance with Inhalational Anesthetics, Support, and Monitoring
Peri‐operative Analgesics
Recovery
Local Anesthetic Techniques
Epidural Anesthesia
Standing Surgery in Donkeys and Mules
Feral, Less Domesticated, and Wild Equids
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